Dissertation - HQ

58 Larvae orientation in situ
that it still lets sound through. High frequency sound can be reduced
to inaudible levels using two nested arenas isolated by a layer of air.
A polarising acrylic filter placed over the chamber can change the
polarisation of light. Eventually, even the magnetic information could
be altered using a solenoid coil placed around the arena (K. Lohmann,
pers. comm.).
Permits to study Compared to the experimental methods used on the reef or in the
younger larval stages laboratory (manipulated light traps 144 or patch reefs 145 , and choice
chambers 103,112,115 ), this device greatly broadens the scope of the experiment.
It makes it possible to study early stage as well as competent
larvae within pelagic waters—their natural environment—instead of
restricting the study to settlement-stage larvae near the reef.
Previous experimental methods only investigated the possibility for
young larvae to detect a particular cue, without any information about
whether it was actually used for orientation. In contrast, in situ methods
showed that larvae orient, but only allow speculation regarding the
cues involved. The OWNFOR method could bring together those two
types of results and allow for an in situ investigation the influence of
environmental cues in the orientation behaviour of all larval stages.
Great efforts have been directed toward modelling larval trajectories and
incorporating larval behaviour in dispersal models 155 . The preliminary
observations made in this study help to emphasise the potential role
of orientation in shaping dispersal trajectories. Given observed current
conditions and swimming bearings, larvae could deviate from passive
trajectories by several hundred meters in as little as 15 minutes, even
under the strong flow speeds in the Gulf Stream (Figure 2.6). The success
and effectiveness of this new device in investigating both orientation
and related cues opens new possibilities for such models and for the
understanding of larval ecology in general.